In pursuit of addition cure silicone adhesives which are adherent to various substrates, one traditional approach is to add tackifiers to curable silicone resins so as to develop adhesive nature. For example, JP-B 53-21026 corresponding to U.S. Pat. No. 3,699,072 discloses an addition cure silicone rubber composition comprising an alkoxysilyl-containing hydrogensiloxane, and JP-B 53-13508 corresponding to U.S. Pat. No. 4,077,934 discloses an addition cure silicone rubber composition comprising an epoxy-containing hydrogensiloxane.
Owing to these development efforts, addition cure silicone adhesives which are adherent to various substrates have been marketed. These silicone adhesives, however, are difficult to adhere to some substrates, especially certain resins. Adhesion may not be developed unless primers are used. Those resins which are substantially non-receptive to the relevant adhesives, referred to as “less-receptive resins,” hereinafter, include polycarbonates and polyphenylene sulfides. There is an increasing need for addition cure silicone adhesives which are spontaneously adherent even to the less-receptive resins.
Known technologies for providing addition cure silicone adhesives which are spontaneously adherent to the less-receptive resins include the addition of nitrogen compounds (JP-B 52-008854 corresponding to U.S. Pat. No. 3,837,876) and the combined use of an alkoxysilane as the tackifier and an organotin, organotitanium, organoaluminum or zirconium compound as the hydrolytic catalyst for the alkoxysilane. However, these technologies can affect the curability of addition cure silicone adhesives. When nitrogen compounds are added to the addition cure silicone adhesives, the catalytic capability of platinum atoms serving as the addition reaction catalyst is substantially prohibited so that the cure process becomes extremely inconsistent. When organotin, organotitanium, organoaluminum or zirconium compounds are similarly added, they deactivate the organohydrogenpolysiloxane in the addition cure silicone adhesives. At elevated temperature, these compounds help cleavage of siloxane bonds in the silicone polymer, causing the cured product to lose heat resistance.